The bridge over the river at NN443578 just before the turn off for Corrour looks a good possibility. I was along that road on my bike last year and didn't see too many other spots. I noticed most of the laybys were blocked off (presumably to prevent overnight car camping). THis can be ignored if you are walking.
This google image is from 2011 before the laybys were blocked.
https://goo.gl/maps/hbnL3xuwmsof59CM9PS - the path across the moor from Black Corrie Lodge gets pretty faint in places but it follows a line of telegraph posts so you can't go wrong.
Lovely spot crossing the moor there.